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  • 1
    Electronic Resource
    Electronic Resource
    A colloidal crystal modeled by bead–spring cubes (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 8182-8195 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In experiments colloidal crystals are usually polycrystalline. This polycrystallinity depends on the shear history, while a stable orientation of the crystallites is obtained by preshearing the sample for a sufficiently long time. To predict the linear viscoelastic properties of a colloidal crystal, the crystallites immersed in a Newtonian fluid are modeled by bead–spring cubes. Explicit constitutive equations are obtained, which describe the stress response on the applied small-amplitude oscillatory shear flow with frequency ω. These constitutive equations are used to predict the dynamic moduli G′(ω) and G″(ω) belonging to the specific configurations of the polycrystalline sample before and after preshearing. The influence of the preshear process on the dynamic moduli is discussed and for a sample that is presheared for a sufficiently long time the following results are obtained: (i) for high frequencies G′(ω) is constant and G″(ω)=η∞ω (where η∞ is the viscosity contribution of the fluid surrounding a crystallite) and (ii) for lower frequencies G′(ω) is nearly constant and G″(ω) is proportional to ω−1/2. The theoretical results obtained in this paper are consistent with experimental results found in literature. It is finally noted that the bead–spring formalism in this paper shows explicitly that the static modulus belonging to the crystallites is identical to the high frequency limit of the storage modulus G′(ω). © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480152
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  • 2
    Electronic Resource
    Electronic Resource
    Shear thinning of suspensions of sterically stabilized spheres studied by Stokesian dynamics simulations (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 2484-2488 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Stokesian dynamics simulations are presented of suspensions of sterically stabilized spheres in a viscous medium, subjected to simple shear. The steric repulsion between the grafted polymer layers of different particles is modeled using an interaction potential that is calculated using a self-consistent field lattice theory. The shear rate dependence and the volume fraction dependence of the suspension viscosity are calculated and compared to experimental data [Nommensen et al. Phys. Rev. E 59, 3147 (1999)]. It is found that shear thinning is mainly caused by the interaction contribution to the viscosity. The present paper, combined with a recent paper of Nommensen et al. [Langmuir 16, 1902 (2000)], shows that computer simulations, theoretical analysis, and experimental work give a consistent physical picture of the rheology of these suspensions when the proper interaction potential is used. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.482066
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  • 3
    Electronic Resource
    Electronic Resource
    The rheological behaviour of suspensions of fat particles in oil interpreted in terms of a transient-network model (1985)
    Springer
    Colloid & polymer science 263 (1985), S. 1008-1024 
    Details
    ISSN: 1435-1536
    Keywords: Suspension ; fat particles ; rheological behaviour ; structured dispersion ; transient-network model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The transient-network model for concentrated dispersions, described in a previous paper, is used to describe the rheological behaviour of dispersions of glyceryl tristearate crystals in paraffin oil. The model prediction of the storage modulus of this system is compared with corresponding expressions given in literature. Model calculations are carried out to fit the linear viscoelastic behaviour of the system as well as its stress response in large amplitude shear experiments. Information is thus obtained about the stiffness and strength of the interparticle bonds, and the chance of them breaking in a state of rest or as the result of flow. It is concluded that the probability of interparticle bond fracture strongly depends on the measure of bond stretching. The general findings link up with the Lennard-Jones potential which is assumed to describe the potential energy of the bonds between the particles. Accurate measurements of the temperature dependence of the dynamic moduli by making use of a torsion resonator lead to the conclusion that the energy dissipation at a high frequency originates mainly from the flow of liquid around the particles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01410995
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  • 4
    Electronic Resource
    Electronic Resource
    The rheological behaviour of suspensions of fat particles in oil interpreted in terms of a transient-network model (1986)
    Springer
    Colloid & polymer science 264 (1986), S. 282-282 
    Details
    ISSN: 1435-1536
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01414967
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  • 5
    Electronic Resource
    Electronic Resource
    A generalized thermodynamic approach to microrheological modelling (1994)
    Springer
    Flow, turbulence and combustion 48 (1994), S. 117-128 
    Details
    ISSN: 1573-1987
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A generalized thermodynamic theory is presented which may be applied to microrheological models. The purpose of this theory is to offer a simple framework for many types of modelling at various levels of description. The essential elements of our approach are: a specification of the subsystem in which the reversible storage of energy takes place, the way of coupling of this subsystem to the environment and a proper definition of reversible and irreversible variables. The resulting set of equations, containing a stress tensor expression a microscopic evolution equation and a microscopic equation of state are expressed in a matrix form. Some applications of the theory to well known micro-rheological models are discussed and directions for further developments are indicated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02027962
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  • 6
    Electronic Resource
    Electronic Resource
    About the torque and energy balances for the flow between eccentric rotating disks (1976)
    Springer
    Rheologica acta 15 (1976), S. 623-627 
    Details
    ISSN: 1435-1528
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Zusammenfassung Die Drehmoment- und Energiebilanzen werden für die Strömung zwischen zwei exzentrisch rotierenden Kreisscheiben (ERD) untersucht. Besondere Aufmerksamkeit verdient dabei die Rolle der Spannungen, die die Ränder der Platten auf die freie Oberfläche ausüben. Es wird gezeigt, daß die Anwesenheit dieser Spannungen wesentlich für die Beurteilung des sogenannten Spannungsenergie-Paradoxes ist. Auch wird der Zusammenhang zwischen diesen Spannungen und den Abweichungen der wirklichen Geschwindigkeitsverteilung von den bisher angenommenen Verteilungen diskutiert.
    Notes: Summary The balances of torque and energy in the flow between eccentric rotating discs (ERD) have been investigated. Special attention has been given to the role of stresses resulting from the forces that are delivered to the free surface by the edges of the plates. These stresses are shown to be significant in considering the so-called stress power paradox. Their role with respect to deviations of the velocity profile from the usually assumed one is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01524748
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  • 7
    Electronic Resource
    Electronic Resource
    A generalized network model for polymeric liquids (1983)
    Springer
    Rheologica acta 22 (1983), S. 539-549 
    Details
    ISSN: 1435-1528
    Keywords: Constitutive equation ; transient-network model ; bead-spring model ; molecular structure ; polymer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract A kinetic model was developed for relating the molecular structure and the rheological behaviour of polymer-like materials in which bonds are being created and broken. In particular, the stress contribution of molecules that are not a part of the network was taken account of. In two limiting cases the model introduced here is identical to the transient-network model and the bead-spring model, respectively. Model predictions were interpreted and compared with measurements on an L.D.-polyethylene melt, available from literature, and an S.I.S.-blockcopolymer solution. In both cases information was obtained about the network and the kinetic processes occurring in a state of rest and during steady-shear flow, assuming the model to be valid.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01351400
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  • 8
    Electronic Resource
    Electronic Resource
    A transient-network model describing the rheological behaviour of concentrated dispersions (1984)
    Springer
    Rheologica acta 23 (1984), S. 329-344 
    Details
    ISSN: 1435-1528
    Keywords: Transient-network model ; stress tensor ; relaxation spectrum ; concentrated dispersion ; conglomerate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Attractive forces acting between particles in dispersions may cause a three-dimensional structure to be built up. A temporary-network model is postulated that describes the rheological behaviour of such systems. Chains of particles are assumed to be created and broken by thermal actions and by applied deformation. The relation between the network structure and the macroscopic stress tensor is deduced. One of the main model features is that no use is made of the common assumption of affinity of the motion of the chain vectors with the gradient of the macroscopic velocity field. Instead, the chain deformations are assumed to depend on the forces acting on them, i.e. their deformations depend on their stiffness and on the applied deformation, whereas fracture of chains may cause stress relaxation in the rest of the network. The chains may behave as highly non-linear springs, whereas the probability that the chains will break in some time interval may be an explicit function of the chain length itself. Integral equations are derived, from which the stress-tensor components can be calculated in any flow experiment, that obeys creeping-flow conditions. Analytical expressions are obtained for the relaxation spectrum of such systems in terms of the microscopic parameters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01329186
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  • 9
    Electronic Resource
    Electronic Resource
    The average stress tensor in systems with interacting particles (1983)
    Springer
    Rheologica acta 22 (1983), S. 4-11 
    Details
    ISSN: 1435-1528
    Keywords: Average stress tensor ; interacting particles ; ensemble averaging ; multiple expansion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The derivation of an expression of the macroscopic stress tensor in terms of microscopic variables in systems of finite interacting particles is discussed from different points of view. It is shown that in volume averaging the introduction of a fictitious “interaction stress field”T I with special boundary conditions on the boundary of the averaging volume is needed. In ensemble averaging similar results are obtained by using a multipole expansion of the local stress and force fields. In the appropriate limiting cases, the obtained results are shown to be consistent with the results of kinetic theories of polymer solutions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01679824
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  • 10
    Electronic Resource
    Electronic Resource
    Stress relaxation due to chain fractures in transient polymer networks (1985)
    Springer
    Rheologica acta 24 (1985), S. 198-201 
    Details
    ISSN: 1435-1528
    Keywords: Stress relaxation ; polymer ; transient-network theory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Aspects of a network model for concentrated dispersions are applied to polymer networks. It is shown how network deformation caused by network fracture affects the macroscopic stress.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01333247
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